Find the value of the expression $\displaystyle{\left({2}{x}-{12}\right)}+{\left(\frac{{1}}{{2}}{x}{y}-{10}\right)}\usepackage{cmbright}\Huge\$ for $\displaystyle{x}={8}\usepackage{cmbright}\Huge\$ and $\displaystyle{y}={2}\usepackage{cmbright}\Huge\$ .